Manufacturing processes



Dec. 15, 1959 5, w J, FORSHAW EI'AL 2,917,613

MANUFACTURING PROCESSES 2 Sheets-Sheet 1 Filed Dec. 30 1957 FIG].

Dec. 15, 1959 Filed Dec. 30 1957 K. G. W. J. FQRSHAW ETAL MANUFACTURING PROCESSES 2 Sheets-Sheet 2 United States Patent MANUFACTURING PROCESSES Kenneth George William James Forshaw, Farnborough, and Cyril Bradbury Charlton, Bromley, England, as signors to Telephone Manufacturing Company Limited, London, England, a British company Application December 30, 1957, Serial No. 705,954 Claims priority, application Great Britain January 2, 1957 3 Claims. (Cl. 219-19) This invention relates to manufacturing processes involving a material consisting of a sheet-like insulating support having deposited thereon a thin metallic film. The support can be paper, synthetic plastic material or the like, which is inherently insulating, or it may be an insulating layer or film on a support. The metallic film can be deposited by a thermal vacuum deposit process, or a chemical process. In the former case the deposit may be, for example, aluminium, cadmium or zinc and in thelatter case, nickel.

One use of material of this kind is for the manufacture of electrical capacitors, when the metal film is used as the electrode of the capacitor. An appropriate number of strips of the material each carrying a metal film on one or both of its major surfaces together with insulating strips, are wound into an assembly.

The metal coated strips are often cut from a wide, completely coated web, but the strips for the capacitors may be required to have the metal coating over less than the whole surface.

The present invention is concerned with an improved method .of and means for removing very thin metal films from an insulating supporting surface. The invention is of general application, but is especially suited for use in the manufacture of electrical capacitors.

In accordance with one feature of the invention there is provided a method of removing portions of metal from selected areas of metallized dielectric material comprising subjecting such areas to a radio frequency fieldof sufiicient strength to vaporize the metal in said areas.

Other features and advantages of the invention will appear from the following description of embodiments thereof, given by way of example, as applied to the pro duction of strip material suitable for the manufacture of electrical capacitors.

In this embodiment a relatively wide web of insulating material such as paper or synthetic plastic is metallized. The metallizing coating is only of the order of 100 millimicrons thick, but is conductively continuous. The web is then slit into narrow strips, of appropriate width.

At the time of slitting, or in a separate re-reeling operation, or at the time when the strips are being wound into capacitor assemblies, parts of the metallizing coating of the strips are removed. For example it may be required to remove one edge of each of two strips, before winding these strips into an assembly, the right hand edge of one strip and the left hand edge of the other being removed.

To remove the unwanted metallizing it is burnt off by means of a radio frequency field. A burn-off roller of appropriate configuration is brought to bear against that part of the strip which is to be removed, whilst the strip is in contact also with at least one other roller, and a radio frequency voltage is applied between the two rollers; if this voltage is sufficiently high the metallizing in contact with the burn-oif roller is vaporized and cleanly removed.

In thepast it has been suggested to remove a metal- ICC lized film by burning ofl' the metallizing, using for this purpose a large conductive roller in contact with the metallizing and a second roller, withlocalized conductive contact with the metallizing, to which rollers a direct current was applied. With this prior method it can occur that small isolated islands of metal are left in the area which was intended to be demetallized. Once such isolated areas were formed, they were no longer in electrical contact with the main body of the metallizing, and so there was no current path to them; once these areas survived the initial current are they would persist.

By using a radio frequency current, on the other hand, current will be induced by inductive or capacitative effects even in isolated conductive areas in the radio frequency field, and so a more complete removal is obtained.

-A further advantage in the use of radio frequency current is that it can be applied as substantially pure radio frequency current, without a direct current component. necessary voltage is of the order of several hundreds of volts, and has to be applied to the rollers from the source through a relatively small resistance. In consequence, the apparatus is dangerous, even lethally so, and has to be carefully protected. On the other hand the radio frequency current can cause only a comparatively mild shock and minor burn injury. Moreover with radio frequency the arrangement is self-exciting.

Various arrangements of rollers can be adopted, and one advantage of the use of radio frequency current is that there is more latitude in this respect than with direct current, since direct contact between the rollers and the metallizing is not essential. In one arrangement the metallized material is passed round the underside of a backing roller; bearing against the metallized surface is the burn-off roller, of appropriate configuration. In contact with the metallizing, one on each side of the burnoff roller, are two further contact rollers. On terminal of the radio frequency supply is grounded; the high potential terminal is connected, through an isolating capacitor if desired, to the burn-01f roller. The contact rollers are connected to ground. With this arrangement there is no radio frequency potential on the metallizing outside the contact rollers, and the risk of shock is accordingly reduced.

In the arrangement of rollers described the backing roller can be insulating or it can be conductive; in the latter case it can be grounded, so that the field'is produced between the burn-off and backing rollers. It may then be more convenient to arrange that the backing roller instead of being cylindrical and engaging the whole width of the strip, engages or is conductive at only the back of the part from which the metallizing is to be removed.

It is not necessary that the backing roller should be in conductive engagement with the metallizing and a capacitative coupling can be used. Thus, a conductive roller can have a very thin layer of a dielectric layer applied to it. For example a layer about a mil thick of polytetrafluoroethylene, applied as a dispersion, can be used.

In a further arrangement of rollers a burn-off roller, as described above, is used in conjunction with two contact rollers also as described. A backing roller is also used and this is conductive or capacitative. In this case the backing and burn-off rollers are connected to the radio frequency supply terminals which are arranged to be in opposite phase with respect to earth. The contact rollers are also at ground potential; this arrangement provides a more intense field at the burn-off point.

In a further arrangement,'two burn-off rollers are used, the backing and contact rollers being as already described. In this case the 'two burn-off rollers are mounted eoaxially a small distance apart (about 1 mm.) and con- With the prior direct current method the 3 nected to opposed phases of the RF. supply to give a more intense field at the burn-off point situated between them.

With the various roller arrangements described, the burn-off roller can be rotated in the direction opposite to that in which the strip is moved, so that any scuffing which occurs assists in the removal of the metallizing.

in accordance with another aspect of the present invention there is provided an improved method of manufacture of capacitors from metallized dielectric.

As explained above, in the manufacture of an electric capacitor from a metallized dielectric an appropriate number of strips or the like of the dielectric, each with a metallic coating one one or both surfaces are wound up into an assembly, together with as many further strips of dielectric as may be necessary for insulation or otherwise.

In carrying out this process the strips are secured to a mandrel, which has to be of comparatively small diameter if, as is usually the case, a capacitor of small dimensions is required, and are wound up together. When the correct length of the strips has been wound, the strips are cut.

The cutting of the strips is not as simple a matter as might at first appear, for the reason that if all the strips are cut simultaneously by a single act there is a danger of a short circuit arising, partly due to the fact that the strips are very thin and consequently the separation between the exposed ends of the metallizing is correspondingly small and partly due to the shearing action which takes place, tending to spread or smear the metallizing across the out face.

To avoid this, it is usual for one electrode strip to be out before the other, and to insert a length of unmetallized dielectric strip between the two electrode layers and then to continue the winding for a few turns so that the unmetallized strip forms a wrapper.

Likewise, for similar reasons, it is usual to offset longitudinally the starting ends of the strips when attaching them to the mandrel. With small value capacitors, requiring a small diameter mandrel, the problem is aggravated by the fact that the interleaving strips may split or crack, again conducive to a short circuit of the electrodes.

The manual complication and consequent expense of winding a capacitor in this way is obvious, and in accordance with a feature of the present invention means are provided whereby the winding is simplified.

In accordance with this aspect of the invention means are provided for burning off the electrode metallizing transversely, near the end of at least one strip and/or the beginning of at least one strip.

In one method of carrying the invention into effect the capacitor is wound and when the appropriate length or number of turns has been completed, or at the correspondrng point before winding is completed, a burn-off electrode is brought into transverse engagement with the strip to remove a band of the metallizing. The electrode can be a roller, and it is a simple matter for this to be done automatically under the control of a turns counter, though a manual control can be used if desired.

Once a strip has been transversely demetallized both electrode strips can be cut to the same length by a single cut, and all the layers of material can be out at this time.

The cut may or may not be effected in the transverse demetallized zone of the one strip but it is advantageous to make the cut at this point for the reason that when the winding of the next capacitor is started the strips can be wound directly without further handling in this respect; the one transverse demetallizing serves to insulate the electrodes of both capacitors. This fact is of great advantage where capacitors are being wound automatically.

The transverse demetallizing can be effected by a roller which serves also for the demetallizing which may be required for other purposes. A sectionalized roller can be used with two or more conductive but insulated areas and burn-olf current, which can be either direct current or high frequency current, fed by means of a switch to the appropriate parts at appropriate times.

It may be convenient or advantageous to effect transverse demetallizing not only on one electrode area but on both or all of them. In this event the demetallized lengths of the strips may be different, but should at least overlap in the region of the cut.

A employing radio frequency currents to effect removal of the metallizing from metallized material will now be described in conjunction with the accompanying drawings of which:

Figure l is a front view of a demetallizing machine.

Figure 2 is a view from the left hand side of Figure 1 showing details of the transmission.

Figure 3 is a sectional view of the exhaust system of the machine.

Figure 4 is a sectional view from the left hand side of Figure 3.

Referring first to Figure 1, there is shown at 1 a radio frequency generator the output of which is taken from an output terminal 2 and applied to demetallizing roller 7 by means of a cable (illustrated by the dashed line). The frequency at which the generator operates can be controlled by a tuning control 3, and the power supply for the generator is connected to an input socket 4-. The construction of the generator itself does not form part of the present invention and is not described in detail.

The web to be demetallized is wound on one of two reels mounted on two reel carriers 8 and passes round four guide rollers 9 the path taken by the web being indicated by a dotted line. One or the other of the reel carriers 8 is driven by means of its associated shaft 27 through the transmission arrangements described later in connection with Figure 2. Between the lower pair of rollers 9 the web passes between a backing roller 10 and the demetallizing roller 7. The latter is detachably mounted at one end of a carrier arm 17 which is urged by a spring 28 to maintain roller 7 in contact with roller 10.

Arm 17 is rotatably secured to one end of a shaft 29 which is adjustable longitudinally by means of a control knob 11 (Figure 2) to traverse the demetallizing roller '7 with respect to the backing roller 10. The latter roller is of electrically insulating material preferably a ceramic material in order to prevent short circuiting of the radio frequency supply when rollers 7 and 10 engage in the absence of a web between them. The two upper rollers 9 are grounded and provide grounding of the metallizing on the web passing between rollers 7 and 10.

The drive motor for the machine is indicated schematically at 5 and the exhausting arrangements described later in connection with Figures 3 and 4 are also indicated schematically in this figure.

Referring now to Figure 2, the drive motor indicated by the chain dotted circle referenced 5, drives through a worm and worm wheel reduction gear (not shown) a transmission arrangement comprising gears 16, 21 and 22, chain and sprocket drives 23 and 24 and two pairs of interengaging gear wheels such as 25, 26 to rotate one or the other of two drive shafts 27 on which the reel carriers 8 are mounted.

The gears 16 can be selectively engaged with gears 21 or 22 by operation of a control knob 15 to drive either shaft 27 through its associated chain and sprocket drive 23 or 24 and each reel carrier 8 is provided with a tension adjusting control 14 serving to control the tension of the web. Speed adjustment and reversal control arrangements not shown are provided for the motor.

The demetallizing roller contacts the metallizing of the web from beneath such web with the result that any metal dust particles which may be formed by the demetalliziug action tend to fall away from the web rather than on to it.

This effect is supplemented by the exhaust arrangements shown in Figures 3 and 4. These comprise an extractor fan 30 driven by a motor 6 and operating to extract air from an exhaust tube 18 of telescopic form. The adjustable part of the exhaust tube 18 is connected by a link 19 to the shaft 29 by which the demetallizing roller 7 is traversed with respect to the backing roller 10 so that the nozzle of tube 18 is maintained close to the point of contact of roller 7 with the Web to be demetallized. As is seen most clearly from Figure 4 this nozzle is arrangedclose to the periphery of roller 7 and metal dust particles formed during demetallizing are sucked into the nozzle and pass through tube 18 into a casing 31 surrounding the motor 6 and fan 30. This casing 31 has at its right hand end in Figure 3 a housing 20 in which is disposed a filter pad serving to remove dust particles from the air as it exhausts from casing 31.

The arrangement of demetallizing roller 7 beneath the web to be demetallized and the provision of the exhausting arrangements combine to reduce to a minimum the risk of any metal dust particles becoming redeposited on the surface from which the metallizing has been removed.

The detachable mounting of the roller 7 facilitates replacement of the roller by other rollers of differing widths so that varying widths of metallizing may be removed as required.

The selective transmission arrangement enables ready handling of reels of metallized material without rewinding no matter which way they have been initially wound, it being necessary to ensure only that the metallizing is on the underface of the web where it travels between the rollers 7 and 10.

The region where the demetallizing takes place may conveniently be enclosed by a transparent or windowed casing as an added safety precaution, the casing being provided with a door which on being opened interrupts the supply of current to the demetallizing roller thus reducing the risk of accidental contact with any part of the machine which is at high potential.

We claim:

1. Apparatus for removing the metallized layer from a selected area of a strip of metallized dielectric material which comprises a radio frequency voltage generator, a first conductive roller and a burn-01f conductive roller, means connecting said first roller to ground, means connecting said burn-off roller to said radio frequency generator, and means feeding said strip across said first roller with One surface of said strip in engagement with said first roller and across said burn-01f roller with the opposite surface of the strip in engagement with said burn-off roller, said radio frequency voltage generator establishing a radio frequency field across said rollers of sufiicient strength to vaporize the metal on said selected area, whereby the leaving of isolated islands of metal on the dielectric material within the selected area is avoided.

2. Apparatus as defined in claim 1 and further including an insulated backing roller positioned directly oppo site said burn-off roller and on the opposite side of the strip therefrom, said backing roller being in engagement with said strip.

3. Apparatus as defined in claim 2, and further including a pair of grounded contact rollers contacting the metallized surface of the strip on opposite sides of said burn-01f roller.

References Cited in the file of this patent UNITED STATES PATENTS 2,113,714 Stein Apr. 12, 1938 2,349,569 Wilson May 23, 1944 2,651,708 Mason et a1. Sept. 8, 1953 2,716,180 Dubilier Aug. 23, 1955 2,766,362 Kinder et al. Oct. 9, 1956 

